There are many applications in industry in which it is desirable to have a pneumatically actuated piston and cylinder structure which is capable of assuming several positions wherein the positions are precisely defined and exactly repeatable. An example of the use of such a device is in the positioning of a mechanical transmission as set forth in U.S. Pat. No. 3,945,265, Bell et al, which issued on Mar. 23, 1976.
The prior art includes various examples of work in this general area, including the above-mentioned Bell et al patent and divisions thereof, as well as the following U.S. Pat. Nos.:
787,479 Tanner PA1 787,480 Tanner PA1 1,372,227 Huggins PA1 1,810,399 Horni PA1 2,137,961 Vorech PA1 2,192,621 Radtke PA1 2,297,026 Sanford PA1 2,244,092 Wheeler PA1 2,506,374 McMahon PA1 2,508,564 Cardwell et al PA1 2,531,907 Daubenmeyer PA1 3,713,364 Francia
With the exception of the Bell et al patent, it is believed that all of these references require either pressure balancing to establish one or more of the positions, or require springs for that purpose, or both. While it is certainly possible to use pressure balancing or multiple pressures to establish multiple piston positions, it is very difficult and requires relatively complicated equipment to be sure that the balance point remains the same each time. Clearly, if it does not, the precise location of the position determined by the balance point is not reliably repeatable. Essentially the same disadvantage is true of springs, in addition to the expense and limited life thereof.
The Bell et al structure therefore represents a significant contribution to the art in that multiple positions can be reached without balancing or springs. There are, however, certain complexities in that structure which make production thereof relatively expensive.